Closed-loop engine control is increasingly being adopted by major engine manufacturers in next-generation engine designs to improve reliability, performance and emissions. A key component of closed-loop engine control is a combustion sensor. The main function of the combustion sensor is to obtain detailed information regarding the quality of in-cylinder combustion including heat release timing (e.g. 10%, 50% and 90%), total amount of apparent heat release from an individual cylinder and in-cylinder pressure. The information can be used in real-time engine control for balancing cylinder load and compensating for fuel system variability.
The most reliable way to obtain in-cylinder combustion information is by measuring in-cylinder pressure directly. There are several techniques for which to measure in-cylinder pressure. However, the cost and durability of existing in-cylinder pressure (combustion) sensors is far from what can be accepted by engine manufacturers. The extra machining required to access the combustion chamber also increases the difficulty of implementing the technology.
Changes in combustion characteristics (heat release) can be due to a number of factors other than change in fuel quantity. For example, a faulty or failed fuel injector can influence combustion by introducing too much or too little fuel into the combustion chamber or introducing fuel at a timing other than what is expected. Changes in fuel quality (heating value) also contribute to combustion characteristic changes. In certain locations around the world, such as in Europe, it is common for fuel quality for gaseous fuels to vary from region to region due to disparate regulating bodies. Existing control techniques employing combustion sensors do not detect these other factors causing changes in combustion characteristics which can impact closed-loop control since the control may not be correcting for the corresponding cause.
The state of the art is lacking in techniques for determining what factors are causing changes in combustion characteristics. The present method and apparatus provide a technique for employing a non-intrusive combustion sensor for fuel system diagnostics in an internal combustion engine.